This invention relates to a high-strength target material that has low permeability and which, hence, is suitable for use in the formation of thin magnetooptical recording films by magnetron sputtering, enabling thin film formation with high utilization factor (the proportion of the target material that is assumed by the amount of thin film formed).
A number of target materials are conventionally used in forming thin magnetooptical recording films by a magnetron sputtering process. Among those many target materials, the one that is described in Japanese Patent Public Disclosure No. 119648/1986 is known to have high strength and it has a structure that consists of:
25-60% (all percentages that appear herein are by area) of an iron-group metal phase composed of at least one metal selected from among Fe, Ni and Co; PA1 10-45% of a rare earth metal phase composed of at least one metal selected from among Tb, Gd, Dy, Ho and Er; and PA1 the remainder being an intermetallic compound phase composed of the phase of reaction between said iron-group metal phase and said rare earth metal phase. PA1 20-75% of a complex phase in which a crystallized iron-group metal is dispersed finely and uniformly in a dendritic, acicular or block form in a proportion of 5-40% (of the total phase) in a matrix composed of an intermetallic compound of at least one rare earth metal selected from among Tb, Gd, Dy, Ho, Tm and Er and at least one iron-group metal selected from among Fe, Ni and Co; PA1 15-40% of a rare earth metal phase composed of at least one metal selected From among Tb, Gd, Dy, Ho, Tm and Er; and PA1 the remainder being an intermetallic compound phase composed of the phase of reaction between said complex phase and said rare earth metal phase.
With the tendency in recent years for forming thin magnetooptical recording films by factory automation with reduced man-power, an extension of the useful life of the target material, or an improvement in its utilization factor, has been strongly needed. To this end, the permeability of the target material has to be further lowered and the craters to be formed in the sputtered surface of the target material must have such a morphology that they extend broadly in a two-dimensional direction and that they are shallow.